Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/20—Exposure; Apparatus therefor
  • G03F7/2022—Multi-step exposure, e.g. hybrid; backside exposure; blanket exposure, e.g. for image reversal; edge exposure, e.g. for edge bead removal; corrective exposure
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/26—Processing photosensitive materials; Apparatus therefor
  • G03F7/265—Selective reaction with inorganic or organometallic reagents after image-wise exposure, e.g. silylation

Definitions

• This invention relates to a high-resolution lithographic method of making monolithic integrated circuits, which comprises the preliminary steps of applying, onto a silicon wafer, a film of a polymeric material incorporating at least one light-sensitive compound, and exposing first areas of the film to an electromagnetic radiation to photochemically generate in a surface layer thereof acid compounds from said light-sensitive compounds.
• a monolithic integrated circuit is basically comprised of a small sheet of a semiconductor material, the so-called “wafer”, wherein the various circuit components are formed as a series of superimposed layers or connection levels.
• the arrangement of the various circuit elements is defined by means of a lithographic process whereby the pattern or "geometry" of the circuit, as previously defined on a glass sheet or light mask, is transferred onto the wafer.
• the wafer is coated with a film of light-sensitive polymer or photoresist having a thickness dimension of about 1 micron.
• the photoresist coated wafer is then exposed, with the interposition of the light mask, to a radiation having a predetermined wavelength effective to produce phisico-chemical alterations in the exposed polymer.
• development This subsequent step of selective removal of the photoresist is customarily referred to in the art by the term "development".
• the latter may be either carried out in a “wet” condition by using suitable liquid reactants, or in a “dry” condition by using suitably ionized, gaseous reactive species.
• a first significant factor entering the definition of ever smaller structures on the wafer is tied to the well-recognized difficulty of optically resolving geometries of a size smaller than 1 micron.
• a second factor in the aforesaid problem is tied to the difficulty of selectively removing, as faultlessly as feasible, predetermined areas of the photoresist, such as those exposed to the radiation.
• the specific prior art has proposed lithographic methods wherein the photoresist is developed in a dry condition by means of an ionized gas plasma comprising oxygen ions as the active species.
• the prior art provides for the use of multi-layered photoresists comprising a first resin layer adapted to evenly cover the topography of the underlying circuit, levelling out any steps therein (planarizing layer), and second surface layer of a light-sensitive resin intended for exposure to the light radiation.
• a further lithographic method developed by the pertinent prior art, and referred to as "image reversal" provides for the use of a single planarizing layer of photoresist which is exposed, in selected areas thereof defined by a light mask, to a radiation having a predetermined wavelength.
• the photoresist in dry developed using an oxygen plasma which will selectively remove the areas without silicon and form a protective layer of SiO2 on the remainder containing it.
• the technical problem that underlies this invention is to provide a lithographic method of making monolithic integrated circuit which can define, on a silicon wafer, patterns of a size equal to 1 micron or lower, and at the same time have a low rate of rejects.
• the photochemically generation of said acid compounds only takes place within a surface layer of limited depth, on the order of 200 to 1000 Angstrom, of the polymeric material or photoresist.
• the net result is the advantageous ability to resolve structures of a smaller size than 1 micro without focusing problems from the presence of steps in the photoresist.
• Resists currently employed comprise a solvent (acetates, ethyl-lactate, etc.), a resin (novolac) and a light-sensitive element (diazo-naphthoquinone).
• polymethyl-methacrylate polymethyl-isopropenyl-ketone
• poly(butene-1-sulphone) poly(styrene-sulphone).
• the light-sensitive compounds incorporated into the polymeric material film are selected from a group having for its base molecule that of quinone, but the substituents may be of varying nature.
• 1,2,5- and 1,2,4-diazo-naphtho-quinone such as the commercially available compounds known as McDermid Ultramac EPA-914-30, Olin-Hunt HPR-­504, or McDermid Ultramac PR-1024-MB-628.
• the above-listed light-sensitive compounds are converted into corresponding indene-carboxylic acid compounds on exposure to a wavelength in the 365 to 436 nanometers range.
• the photoresist is preferably subjected to 70-90 successive exposures, each lasting 100-500 ms, at temperature of about 25°C. Specifically, during each exposure, two or three devices will be defined by the light mask, each occupying different areas of predetermined size on the wafer. On completion of the exposure steps, there will be defined thereby on the wafer 140 to 270 devices.
• said neutralization of these acid compounds is accomplished after diffusing through the photoresist film basic compounds having a low molecular weight.
• low molecular weight amines such as ammonia, methylamine, mono- or di­ethylamine, and halogenated derivatives thereof are the preferred ones.
• the temperatures and times for the neutralization step may be selected within the ranges of 60° to 100°C and 35 to 50 minutes, respectively.
• the incorporation of silicon to the photoresist is only performed after neutralizing, in said surface layer, the acid compounds generated during exposure.
• the photoresist In order to favor the diffusion of silicon through the photoresist, and its incorporation thereto, the photoresist is once again exposed to light so as to form the aforesaid acid compounds in a surface layer of the previously unexposed areas.
• the acid compound will react, during the next method step, with a basic molecule comprising silicon, following diffusion thereof through the photoresist film.
• TMCS trimethylchlorosilane
• HMDS hexamethyl-disilazane
• silylation of the photoresist will only affect a surface layer thereof in the 200 to 1000 Angstrom range.
• the working conditions for silylation are a temperature within the range of 100° to 180°C, a pressure in the 5 to 30 Torr range, and a duration in the 2 to 50 minutes range.
• the final step of dry developing the photoresist takes place under the customary conditions, well-known in the art, for RIE (Reactive Ion Etcher) or MIE (Magnetron Ion Etcher) development techniques.
• RIE Reactive Ion Etcher
• MIE Magnetic Ion Etcher
• the method of this invention thus enables, advantageously and contrary to what the prior art could afford, an almost complete utilization of the selective etching properties of development by plasma.
• a set made up of twenty five silicon wafers were subjected, using conventional techniques, to coating with a novolac-based resist to yield a film approximately 2.2 micron thick.
• the photoresist employed incorporated 1,2,4-diazo-naphthoquinone as the light-sensitive compound.
• the wafers were then introduced into an exposer ASML 2500 I-line Stepper, and exposed, one at a time, to an electromagnetic radiation at a wavelength of about 365 nm following interposition of an appropriate light mask including the image of two devices. More specifically, each wafer was subjected to seventy successive exposure frames to transfer a total of 140 devices onto the entire surface of the wafer. Each exposure had a duration time of about 250 ms.
• the temperature and pressure within the exposing apparatus where maintained under ambient conditions (25°C, 1 atm).
• the wafers were maintained at a temperature of 80°C and a pressure of about 3 Torr for approximately 45 minutes in an environment saturated with ammonia vapors.
• the wafers were taken out and their surface again exposed, this time with no intervening light mask, to an electromagnetic radiation having a wavelength of from 300 to 400 nm (broad band).
• the exposing apparatus employed was a Model Autoflood 1000 from OAI (Optical Associate Instrument).
• SVG Silicon Valley Group
• Model 86 XX Model 86 XX
• the basic molecule used for diffusion was hexamethyl-­disilazane fed continuously into a module PSVG (Primer Silicon Valley Group) for silylation at a volume flow rate of about 13 cubic centimeters per minute.
• PSVG Primary Silicon Valley Group
• the temperature and pressure were controlled at 150°C and 10 Torr, respectively, during silylation.
• the overall silylation time was of about 2 minutes.
• the silicon wafers were then taken, for the final development step, to a developing apparatus, Model Tegal 1511, wherein an oxygen plasma was generated using RF at about 13.56 MHz.
• the wafers were checked to find out possible faults and ascertain that the degree of resolution sought had been achieved.
• the method described hereinabove enabled a structure of 0.7 microns in size to be transferred onto the wafers. Out of a total of twenty five wafers, each including 140 devices, about 50% of the devices were found to be free of faults and passed on for further processing.
• the method of this invention has proved to be uniquely suitable to provide for reproduction of structures measuring less than one micron in size on wafers, at a low rate of rejects.
• the output of faultless devices can be as high as 50% approximately, as against the levels of 30-40% afforded by lithographic methods according to prior art tecniques.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Inorganic Chemistry (AREA)
• Organic Chemistry (AREA)
• Photosensitive Polymer And Photoresist Processing (AREA)
• Exposure Of Semiconductors, Excluding Electron Or Ion Beam Exposure (AREA)

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Publications (2)

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Family Applications (1)

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Cited By (2)

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• 1989
  • 1989-08-10 IT IT8921496A patent/IT1231108B/it active
• 1990
  • 1990-07-17 EP EP19900113668 patent/EP0412326A3/en not_active Withdrawn
  • 1990-07-26 JP JP2196390A patent/JPH0395560A/ja active Pending

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